Apparatus for electrostatically treating extruded polyethylene film and the like



1965 1. L. NELSON 3,200,313

APPARATUS FOR ELECTROSTATICALLY TREATING EXTRUDED POLYETHYLENE FILM ANDTHE LIKE Filed Feb. 21, 1962 2 Sheets-Sheet 1 420 F/& j

INVENTOR [use L. NELSON ATTORNEY 3,200,313 DED I. L. NELSON Aug. 10,1965 APPARATUS FOR ELEGTROSTATICALLY TREATING EXTRU POLYETHYLENE FILMAND THE LIKE Filed Feb. 21, 1962 2 Sheets-Sheet 2 INVENTOR IVER Z.Alas'o/v BY gi flphmanmj ATTORNEY United States Patent 3,200 313APPARATUS FUR ELECTiQGSTATlCALLY TREAT- ENG EXTRUDED POLYETHYLENEFiLll/l AND THE MIKE liver L. Nelson, Minneapolis, Minn, assignor toWaldorf Paper Products Company, St. Paul, Minn., a corporation ofMinnesota Filed Feb. 21, 1962, Scr. No. 174,846 6 Claims. (Cl. 317-262)This invention relates to an improvement in method and apparatus fortreating extruded polyethylene film and and the like, and dealsparticularly with the use of a di electric blanket which may be used inthe treatment of the film with high frequency current.

Various means have been employed for treating the surface of extrudedpolyethylene film to produce a surface which may be more readily printedand glued. In some instances, a coating is applied to the surface forthe accomplishing of this purpose. In other instances, the surface ofthe film is oxidized by directing a high frequency current toward thesurface, the oxidation of the surface improving its printability andalso its receptivity to adhesives. in most instances, this isaccomplished by supporting an el ctrically conductive treating bar inclose proximity to the surface of the film, and applying the highfrequency current to this treating bar and to the roller over which thefilm is conveyed. In order to prevent the static electricity frompassing through the film and causing pin holes therein, the roller ispreferably covered with a dielectric surface which may be glass orcertain plastic which overlies the roll and prevents the arcing of thecurrent through the film.

One of the difficulties encountered in this process lies in the factthat considerable time is required to change such dielectric rollers inthe event the roller becomes damaged so that the electricity may arcthrough the film. Furthermore, rollers of this type are usually quiteexpensive to produce. One of the difficulties involved lies in the factthat there is considerable time and money involved in starting up anextruder and when the dielectric roller is defective, it is normallynecessary to completely shut down the extruder for several hours untilthe roller can be replaced. It has been attempted to pass the film overa fixed dielectric surface. However, this has been found generallypractical as the fixed dielectric surface is readily injured by the highfrequency current continuously directed toward the same fixed surface.

An object of the present invention resides in the provision of adielectric comprising a flexible blanket of plastic material which ispositioned to overlie a roller over which the treated film is directed.Means are provided for oscillating this blanket back and forth over theroller so as to continually provide a different portion of the blanketbetween the treating rod and the roller. The blanket is provided withmeans to simplify the attachment to the apparatus so that in the eventthe blanket becomes damaged, it may be changed in a very short period oftime. As a result, the extruder may merely be moved out of alignmentwith the apparatus for the time necessary to remove one blanket and toattach another and little time and only a small amount of film formingmaterial is lost.

A feature of the present invention resides in the provision which isattached to the apparatus adjacent to the roller over which the film isto be directed and to provide means for oscillating this frame duringoperation of the apparatus. The dielectric blanket is attached atopposite ends to opposite sides of the frame, and upon oscillation ofthe frame, the blanket is drawn first in one direction and then theother to continuously change the portion of the surface of the blanketwhich is between the treating bar and the roller.

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or in These and other objects and novel features of the presentinvention will be more clearly and fully set forth in the followingspecification and claims.

in the drawings forming a part of the specification;

FIGURE 1 is a side elevational view of a portion of a film extrudingapparatus, showing the arrangement of the treating apparatus.

FIGURE 2 is a perspective detail of the treating unit.

FIGURE 3 is a plan view of the blanket in flat form.

FIGURE 4- is a perspective detail showing the manner in which one edgeof the blanket is secured to the frame.

FiGURE 5 is a perspective detail showing the manner in which the secondedge of the blanket is secured to the frame.

FIGURE 6 is a sectional view through a portion of the treating bar androller, and showing the dielectric blanket between the film and thesurface of the roller or drum over which the blanket oscillates.

FEGURE 1 discloses a portion of the outlet end of an extruder A whichis, in the arrangement illustrated, designed to extrude a film ofpolyethylene or other suitable such coating to a web of paperboard. Theextruder is not illustrated in detail, as such devices are well known inthe art. A portion of the extruder frame it is designed to support thecooling drum i1, and in the arrangement illustrated, the plastic film isextruded between the web of paperboard and the polished surface of thedrum if, the coated web being indicated at 12 with the surface of thefilm leaving the smooth surface of the roll 11. The web passes over apair of idle rollers 13 and 14 and is then directed downwardly aroundthe guide rollers 15 and 16, which in the particular arrangementillustrated, are supported near the floor so that the platform orcatwalk 17 may extend across the frame above the film.

In the particular arrangement illustrated, the frame It) is separatedinto the main section ill which is identified by that numeral, and awinding frame section 19 which supports the rewinding apparatus, notillustrated in the drawings.

An auxiliary frame portion 2% is interposed between the frame sections1% and 1% and includes an upright standard 21 which supports a treatingroll or drum 22. The web 12 extends upwardly over the treating drum 2.2and then around idle rollers 23 and 24 which are also supported at a lowelevation so that a second platform or catwalk 25 may extend across theframe.

As is perhaps best illustrated in FIGURE 2 of the drawings, a generallyrectangular frame is supported beneath the treating roller 22. The frame26 includes a pair of parallel end members 27 and 29 which are connectedby a pair of parallel angle members 39 and 31. A supporting shaft 32extends centrally through the end members 27 and 29 in parallel relationto the angles 3t and 31. The shaft 32 is supported by suitable bearingssuch as 33 which are mounted upon the standards 21 of the auxiliaryframe 2t). The angle members 3% and 31 are provided with coplanaroutwardly directed flanges 34 and 35 respectively through which thedielectric blanket B is anchored.

The dielectric blanket B may be formed of a single layer of dielectricmaterial; but in the particular arrangement illustrated, the blanket isformed of a series of laminations of a material commercially known asMylar which are connected together along opposite ends. As indicated inFIGURE 3 of the drawings, the blanket B is provided with a first seriesof grommets 37 along one edge thereof, and a second similar series ofgrommets 39 along the opposite edge of the blanket. The blankets B aremade up in advance so that in the event one dielectric blanket isinjured, another similar blanket can be substituted in a relativelyshort period of time.

As is indicated in FEGURE 4 of the drawings, the

outwardly extending flange 35 of the angle frame member 31 is providedwith a series of spaced eyebolts 40 which are anchored to the flange 35by any suitable means such as by the nuts 41. Generally S-shaped hooks42 connect the spaced eyebolts 40 with the correspondingly spacedgrommets 37 along one edge of the blanket to anchor the blanket to oneside 31 of the frame. As is indicated in FIGURE of the drawings, theflange 34 of the other frame side 30 is provided with a second series ofsimilar spaced eyebolts 43 which are anchored to the flange 34 by nuts44 or other suitable means. Tension springs 45 are provided at one endwith hook ends 46 designed to extend through an eyebolt 43 and at itsother end a hook shaped member 47 designed to extend through acorresponding grommet 39 in the blanket B. In attaching the blanket, oneedge of the blanket is connected to the frame side 31 by the hooks 42and the other end is then attached to the side 30 by the springs 45, theblanket being drawn taut about the periphery of the treating drum 22.

An elongated block 49 of insulating material is suspended above the roll22 by any suitable means such as that illustrated in FIGURES 2 and 6 ofthe drawings. The block 49 is provided with a pair of upwardly extendingears 50 through which a suspension rod 51 extends. The rod 51 issupported between suitable sockets 52 in the frame standards 21. Theblock 49 is provided with a groove 53 extending throughout its lowersurface and designed to accommodate the conductive heating bar or rod54. The rod 54 is anchored in the groove 53 by any suitable means suchas by studs 55 which are secured thereto and which extend throughapertures in the block 49 and held in place by nuts 56.

The coated web includes a base sheet 57 of paperboard 'or similarmaterial, and a coated layer 59 of polyethylene or other suitable film.As is evident from FIGURE 6 of the drawings, the blanket B underlies thebase sheet 57 and the application of high frequency current between themetal drum 22 and the treating bar 54 produces a discharge from thesurface of the bar 54 which oxidizes the surface of the film 59. Thecurrent is prevented from arcing through the coated sheet by thedielectric blanket 12.

Suitable means are provided for oscillating or rocking the frame 26about its supporting shaft 32. In the particular arrangementillustrated, the motor 69 drives a gear reduction 61 which rotates acrank disk 62. A connecting rod 63 is eccentrically pivoted to the disk62 at 64 and has its other end pivoted at 65 to an arm 66 mounted uponthe frame shaft 32. Upon rotation of the disk 62, the arm 66 isoscillated between fixed limits, thus rocking the frame 26 first in onedirection and then another.

The drum 22 is normally rotated first in one direction and then in theother by its engagement with the blanket B. The web 12 slips over thesurface of the smooth blanket B and is drawn between the treating bar 54and the drum 22. The corona which is given off by the high frequencytreating bar 54 tends to oxidize the surface of the film 59 as it passesbeneath this bar.

The process of treating the film in general is similar to that describedin an article by I C. Van Der Heide and H. L. Wilson printed in the May1961 issue of Modern Plastics. An alternating voltage generator 70 isconnected by a conductor 71 to the treating bar 54 (through thesupporting bolts 55), and by a conductor 72 including a suitableresistance 73 to ground at 74 and to the metal roller 22 which isnormally grounded. The electrode 54 produces a corona discharge betweenthe electrode and the dielectric blanket B, or the polyethylene filmtraveling over the lanket B. The dielectric blanket prevents the currentfrom arcing through pin holes in the film which would act to enlargethese pin holes.

In accordance with the patent statutes, I have described the principlesof construction and operation of my improvement in apparatus forelectrostatically treating extruded polyethylene film and the like, andwhile I have endeavored to set forth the best embodiment thereof, Idesire to have it understood that changes may be made within the scopeof the following claims without departing from the spirit of myinvention.

I claim:

1. An apparatus for treating an extruded thermoplastic film theapparatus including a metal roller, a blanket of dielectric materialpartially wrapped about said roller, means for moving said blankettangentially of said roller first in one direction and then in theother, means for directing the film to be treated over the roller anddielectric blanket, an electrode supported parallel to, and slightlyspaced from, the portion of the sheet over which the film is directed,and a current generator connected between said electrode and said rollerfor creating a corona discharge between the electrode and the dielectricblanket.

2. The apparatus of claim 1 and in which the means for moving theblanket includes a pivotally supported frame to which the ends of theblanket are secured.

3. The structure of claim 1 and in which the means for moving theblanket includes a generally rectangular frame, and means intermediatethe sides of said frame for pivotally supporting said frame, and meanssecuring said blanket to opposite sides of said frame.

4. The structure of claim 1 and in which the means for moving theblanket comprises a member having parallel sides, means supporting saidmember for pivotal movement on an axis midway between said sides, meansfor connecting opposite ends of said blanket to said sides, and meansfor rocking said member about said axis.

5. In combination with an apparatus for extruding polyethylene filmincluding a series of rollers over which said film is drawn and a filmsurface treating device including an electrode supported in spacedrelation to the film surface and a current generator connected between aconductive roller and said electrode, a dielectric blanket between saidfilm and said conductive roller, and means for moving said blanket oversaid surface first in one direction and then the other.

6. The structure of claim 5 and in which the means for moving theblanket comprises a frame pivotally supported on an axis parallel tosaid conductive roller axis, and means securing the ends of said blanketto said frame on opposite sides of the pivot axis, and means for rockingsaid frame about said pivot axis.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL BERNSTEIN,Primary Examiner,

1. AN APPARATUS FOR TREATING AN EXTRUDED THERMOPLASTIC FILM THEAPPARATUS INCLUDING A METAL ROLLER, A BLANKET OF DIELECTRIC MATERIALPARTIALLY WRAPPED ABOUT SAID ROLLER, MEANS FOR MOVING SAID BLANKETTANGENTALLY OF SAID ROLLER FIRST IN ONE DIRECTION AND THEN IN THE OTHER,MEANS FOR DIRECTING THE FILM TO BE TREATED OVER THE ROLLER ANDDIELECTRIC BLANKET, AN ELECTRODE SUPPORTED PARALLEL TO, AND SLIGHTLYSPACED FROM, THE PORTION OF THE SHEET OVER WHICH